It is well known that incorporation of discontinuous fibers with polymeric materials can impart improved properties such as greater strength and stiffness to the polymer matrix. Such materials are described, for example, in U.S. Pat. No. 3,764,456 to Woodhams and in U.S. Pat. No. 4,442,243 which describes reinforced mica-thermoplastic composites having improved physical properties and durability. The combination of discontinuous cellulosic fibers with a variety of vulcanized elastomers is described in U.S. Pat. No. 3,697,364 to Boustany and Coran.
The use of inorganic fillers such as mica and glass fiber possess many difficulties during the fabrication. Due to its abrasive nature these fillers cause more wear to the processing machinery and also since these fillers are brittle they suffer extensive breakage during compounding. Many of the above mentioned problems can be greatly reduced when organic fillers were used. The great abundance and cheapness of cellulosic materials make them one of the attractive choice as a low cost fillers in polymers. The published literature contains number of references for the use of cellulosic fillers as additives for both thermosets and thermoplastic polymers.
Although the use of cellulosic fillers in thermoset resins has been known for decades, their use in thermoplastics has been limited as a result of problems in dispersing the filler in thermoplastic matrix and the lack of chemical bonding between the filler and polymer matrix. It has been shown by Hamed in U.S. Pat. No. 3,943,079 that the dispersion of discontinuous cellulosic fibers in the polymer matrix can be greatly improved by pretreatment of the fibers with a polymer and a lubricant. The French Patent No. 76,34301 describes the preparation of a new material, property of which can be adjusted to adaptation of different applications, which can be formed by a copolymer or a by grafting in a manner that can play a reinforcement role to the polymer.
Goettler in U.S. Pat. No. 4,376,144 has shown that the adhesion of discontinuous cellulose fibers to a matrix of vinyl chloride polymer can be substantially improved by incorporating therewith a bonding agent which is a cyclic trimer of toluene diisocyanate. The bonding agent also improved the dispersibility of the treated fibers into the matrix material. The bonding agent has been found effective at relatively low concentrations-as low as 0.1 parts by weight on 100 parts by weight of the vinyl chloride polymer in the matrix. Coran and Patel have found that U.S. Pat. No. 4,323,625, treated fibers comprising discontinuous cellulosic fibers of aspect ratio greater than five, and methylol phenolicmodified crystalline polymer from alpha olefin monomer having 2-4 carbon atoms, said modified crystalline polymer being present in an amount sufficient to reduce fiber-to-fiber interactions up to about 85 parts by weight per 100 parts of fibers by weight, have useful properties. Advantageously, the fibers can be oriented to a greater or less degree, providing products having a greater strength and stiffness in the direction of orientation.
Gaylord described in U.S. Pat. No. 3,645,939 a process for compatibilizing a material containing free hydroxy groups with a polymer which is otherwise incompatible, by bringing them together in the presence of an ethylenically unsaturated carboxylic acid, substituted carboxylic acid or carboxylic acid anhydride and a preradical precursor or preradical generating agent. Lochowicz et al., in U.S. Pat. No. 4,107,110 described that cellulose fibers, coated with a grafted copolymer comprising 1,2-polybutadiene to which is grafted an acrylate such as butylmethacrylate could be used in reinforcing of polyethylene and other plastic compositions.